The present invention relates to a unified method, apparatus and product arrangement for producing nanofiber filaments and more particularly, to such an arrangement for producing organic filter media nanofibers.
It is well known in fiber manufacture to produce extremely fine fibrous materials of organic fibers, attention being directed to U.S. Pat. No. 4,043,331 and U.S. Pat. No. 4,044,404, issued to G. E. Martin et al on August 23 and August 30, respectively, wherein a fibrillar mat product is prepared by electrostatically spinning an organic material and subsequently collecting spun fibers on a suitable surface; U.S. Pat. No. 4,266,918, issued to R. S. Manley on May 12, 1981, wherein a controlled pressure is applied to a molten polymer which is emitted through an orifice of an energy charged plate; and, to U.S. Pat. No. 4,323,525, issued to A. Bornat on Apr. 6, 1982, wherein a water soluble polymer is fed by a series of spaced syringes into an electric field including an energy charged metal mandrel having a sheath of aluminum foil wrapper therearound which may be coated with PTFE (Teflon™) release agent. Attention is further directed to U.S. Pat. No. 4,044,404, issued to G. Ernest on Aug. 30, 1977, U.S. Pat. No. 4,639,390, issued to R. Shoji on Jan. 27, 1987; U.S. Pat. No. 4,657,743, issued to A. C. Fisher on Apr. 14, 1987; U.S. Pat. No. 4,842,505, issued to D. Annis et al on Jun. 27, 1989; U.S. Pat. No. 5,522,879, issued to A. G. Scopelianos on Jun. 4, 1996, U.S. Pat. No. 6,106,913, issued to F. L. Scardino et al on Aug. 22, 2000; and, U.S. Pat. No. 6,111,590, issued to S. Zarkoob et al on Aug. 29, 2000—all of which use polymer nanofiber production arrangements. Finally, attention is directed to the nanofiber polymer spinning article entitled, “Development of Non-wovens for Protective Clothing: “Nanofiber Membrane Example”, by P. Gibson et al, published on 9th Annual TANDEC Nonwovens Conference, Nov. 10–12, 1999 by the U.S. Army Soldier Systems Center, Natick Mass.
In all of the above prior art, none—either alone or in combination—recognizes let alone teaches, the novel, unified electro-spinning method, apparatus and product arrangement hereinafter set forth. In accordance with the present invention, it is recognized that solvent recovery is a most critical issue, since solvents for most polymers are organic and harmful. Moreover, the fiber tensile strength has proven to be very low with the produced fibers dissolving in water, including environmentally humid conditions. The continuous, uninterrupted manufacturing process of elecrospinning is an important feature of the present invention. A further feature of the present invention is to provide for uniform coverage across a full width of a product through the novel usage of multiple capillary tubes. To further increase production output, the present invention recognizes the advantages of manufacturing tubular capillary tubes with sharp plural outlet tips and with the application of heat surrounding the capillary tubes to further improve output. The present invention, recognizing these past problems in the electro-spinning of water soluble polymeric material, provides a unique arrangement wherein nanofibers can be significantly reduced to very thin cross-sectional areas and yet be produced under unique alternative pressure steps, resulting in a comparatively stronger and more flexible nanofibers. The nanofibers produced by the unique electro-spinning arrangement of the present invention allow for a safe environment with the produced nanofibers being comparatively stronger and having good adhesion and flexibility when mounted to a substrate, allowing for a minimum increase of pressure drop across the manufactured product. In addition, products produced by the unique electro-spinning arrangement of the present invention maintain a comparatively high porous integrity with such lower pressure drop, resulting in higher product efficiency—particularly of significance in the environmental fluid filtration arts. The unique properties of fibers are arrived at in the present invention by combining selected greater portions by weight of water soluble polymers with a selected lesser portion by weight of cross-linkable agent capable of forming three dimensional structural unit molecules with the balance by weight being water. In accordance with the present invention, a selected acid can be added to increase the rate of chemical cross-linking. In addition, heat or ultra violet (UV) light can be applied to enhance cross-linking reaction as the nanofibers are formed. In some selected instances the novel nanofibers can be collected on an acid-water soaked substrate.
Various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth herein.